Exploring the Early Phase of Crohn's Disease

The Underappreciated Role of Secretory IgA in IBD

Eighty percent of antibody secreting cells (ASCs) are found in the intestine, where they produce grams of immunoglobulin (Ig) A daily. immunoglobulin A is actively transcytosed into the lumen, where it plays a critical role in modulating the gut microbiota. Although loss of immune tolerance to bacterial antigens is the likely trigger of the dysregulated immune response that characterizes inflammatory bowel disease (IBD), little effort has been placed on understanding the interface between B cells, IgA, and the microbiota during initiation or progression of disease. This may be in part due to the misleading fact that IgA-deficient humans are mostly asymptomatic, likely due to redundant role of secretory (S) IgM. Intestinal B cell recruitment is critically dependent on integrin α4β7-MAdCAM-1 interactions, yet antibodies that target α4β7 (ie, vedolizumab), MAdCAM-1 (ie, ontamalimab), or both β7 integrins (α4β7 and αE [CD103] β7; etrolizumab) are in clinical use or development as IBD therapeutics. The effect of such interventions on the biology of IgA is largely unknown, yet a single dose of vedolizumab lowers SIgA levels in stool and weakens the oral immunization response to cholera vaccine in healthy volunteers. Thus, it is critical to further understand the role of these integrins for the migration of ASC and other cellular subsets during homeostasis and IBD-associated inflammation and the mode of action of drugs that interfere with this traffic. We have recently identified a subset of mature ASC that employs integrin αEβ7 to dock with intestinal epithelial cells, predominantly in the pericryptal region of the terminal ileum. This role for the integrin had not been appreciated previously, nor the αEβ7-dependent mechanism of IgA transcytosis that it supports. Furthermore, we find that B cells more than T cells are critically dependent on α4β7-MAdCAM-1 interactions; thus MAdCAM-1 blockade and integrin-β7 deficiency counterintuitively hasten colitis in interleukin-10-deficient mice. In both cases, de novo recruitment of IgA ASC to the intestinal lamina propria is compromised, leading to bacterial overgrowth, dysbiosis, and lethal colitis. Thus, despite the safe and effective use of anti-integrin antibodies in patients with IBD, much remains to be learned about their various cell targets.

A scoping review on early inflammatory bowel disease: definitions, pathogenesis, and impact on clinical outcomes

BACKGROUND

Crohn's disease (CD) and ulcerative colitis (UC) arise from a dysregulation of the balance between commensal microbiota and mucosal-associated immune system, in patients with genetic and environmental predisposition. Different pathophysiological mechanisms have been reported to influence disease history, with impact on disease phenotype and risk of complications.

OBJECTIVES

This review aims to summarize the definitions of early CD and UC, analyze the underlying immunological mechanisms, and evaluate the impact of recognizing and treating early inflammatory bowel disease (IBD) on patients' prognosis (short- and long-term outcomes).

DESIGN

To address this issue, we have performed a scoping review.

DATA SOURCES AND METHODS

Three online databases (MEDLINE, Web of Science, and ScienceDirect) were searched and the results were independently screened by two reviewers.

RESULTS

From 683 records identified, 42 manuscripts evaluating early IBD in adult patients were included. The 'early CD' concept was first described in 2008. Four years later, an international consensus proposed the definition of diagnosis up to 18 months, in patients without previous or current need for disease-modifying therapies. Several other definitions have been proposed; the '2 years since diagnosis' is the most used, regardless of disease characteristics or medication. The amount of evidence on early UC is lower and more recent. Regarding early disease pathogenesis, most theories emphasize the prominent role of innate immunity, followed by early-Th1 adaptive response.

CONCLUSION

The treatment of early CD seems to be crucial for the management of CD patients, impacting short-, medium-, and long-term outcomes. On the other hand, the early treatment of UC appears to be less advantageous, yet evidence comes from only a few retrospective studies.

Novel trends with biologics in inflammatory bowel disease: sequential and combined approaches

Inflammatory bowel disease (IBD) management has changed dramatically over the past 20 years, after the introduction of targeted biological therapies. However, the impact of these new drugs in changing the natural history of disease is still under debate. Recent evidence seems to suggest that the extent of their efficacy might be, at least partially, dependent on the timing of their introduction and on the subsequent management strategy. In this complex landscape, the potential role for a more dynamic approach with treatments based on sequencing and combining targeted therapies has been explored only minimally so far. In this review, we aim to explore the potential biological rationale behind the use of sequential and combination therapies in IBD, to summarise the current knowledge on this topic and to propose a management algorithm that combines these notions.